Episode 190 – European Eel: Mystery Cycles

“…and today we’re talking about an ocean journey that puts Finding Nemo to shame! But more on that later…”

Some animals are born, live, and die in one place. Their homes are never far away and they’re familiar with all they survey. But some species travel great distances, driven by some unknown impulse. A journey can change you, and it does just that for the European eel. But their travels force them from carefree days in sunny streams, into the shadows of the sea. But in the end it’s only a passing thing, this shadow, even darkness must pass in Life, Death, and Taxonomy.

Measure Up 

Welcome to the beloved Measure Up segment. The official listener’s favorite part of the show! The part of the show when we present the animal’s size and dimension in relatable terms through a quiz that’s fun for the whole family. It’s also the part of the show that’s introduced by you when you send in audio of yourself saying, singing, or chittering the words Measure Up into ldtaxonomy at gmail dot com. We do have a new Measure Up intro!

Length

  • Their upper end is 1 m (3 ft 3 in). Some have been found over 4 ft.
  • How many European eels go into the length of the USS Cyclops?
  • Hint: The ship went missing in 1918 on a trip between Salvador in Brazil and Baltimore, Maryland. It is thought that a combination of a cracked engine part, overloaded cargo, and bad weather sank the ship, but no wreckage has ever been found. 
  • 165 eels. The ship was 542 ft (165 m) long. 

Lifespan

  • They can live up to 80 years but one specimen called the Brantevik Eel lived to be 155.
  • How many Brantevik Eel ages would it take to cross the Milky Way Galaxy at lightspeed?
  • Hint: The Milky Way is where you and I and all the animals we’ve ever covered live.
  • 645 eel ages. It would take around 100,000 years to cross the galaxy at lightspeed.

Fast Facts

  • Range: Lives in the lakes and rivers of Western Europe, Russia, Scandinavia, and even North Africa and Turkey.
  • Diet: fish, mollusks, crustaceans, insects, worms.
  • Behavior:
    • They can climb dams and even go up on land for short periods to eat slugs and worms.
    • Eels can live up to 85 years in captivity with one Swedish eel lived for 155 years
    • They are critically endangered, but researchers aren’t sure why. One potential factor is the number of dams that have been built in Europe (over 24K). The eels can climb dams but this drastically impedes their migratory life cycle.
      • They have also been used as food in the past and may still be exported to Asian markets
  • Catadromous – migrating from fresh water to the sea to spawn

Major Fact: Called to the Sea

Where do eel babies come from?

It’s a question that has baffled science for ages, all the way back to Aristotle, who thought they spontaneously grew out of the mud.

A Tik Tok account called Colethesciencedude brought this to internet attention. But he leaves out a major fact about the European eel that makes this phenomenon sound way more mysterious: They have a complex life cycle with six different stages.

We know a bit more about eel reproduction that Cole leads us to believe, but eel reproduction is still weird and amazing. 

Cole also mentions their reproduction “has to do with the bermuda triangle,” which makes this eel even more mysterious. 

Technically, they go to the Sargasso Sea, which is an area of the Atlantic Ocean that overlaps with the Bermuda triangle, but also includes miles of ocean North and east of the Bermuda triangle. The sargasso sea is an area of ocean that has four currents that form an ocean gyre, or a giant circle. 

These unique conditions make that part of the ocean weird. Most notably, it often sees very little to no wind movement, which vexed early sailors. The sea also has a unique type of seaweed called sargassum seaweed, which is the nastey slimy seaweed that tickles your leg and freaks you out whenever you swim on the Atlantic coast.

Between the lack of wind and the tangle of seaweed that sailors thought could gum up boats, the sargasso sea came to be known as cursed, and it’s often linked to Bermuda triangle lore. 

But the seaweed is what’s very interesting to our friend the eel. Eels start life as eggs in the seaweed in the middle of the sargasso sea. They hatch as flat, transparent, larvae called leptocephalus. These little leaf-shaped larvae are carried eastward on ocean currents toward Europe.

It takes them two years to get there and they can travel as much as 6000 km. When they reach coastlines… “What? Leptocephalus is evolving?”

The eel changes to it’s next form called a glass eel. They’re still transparent, but they take on a more familiar eel shape. A handful looks like rice noodles. 

They hang out on the coast until they are ready to move inland upstream. But before they do that, they have to go into stealth mode. They change once again into a stage called an Elver which are brown and better at camouflaging in in-land streams. 

Elvers are relentless in their journey. They may come out of the water to cross fallen branches or rocks that block their path. They may even cross land like a bullseye snakehead.

Once they find a nice two bed two bath home with a white picket fence, they stay there to eat and grow. This is when they enter their next stage called yellow eels. They stay like this for up to 20 years. 

At some point, they start to feel the sea-longing and heed the call of the Valinor and begin their journey into the west. At this point, they turn into silver eels because “all will fade to silver glass, a light on the water all souls pass…”

Amazingly, their body chemistry changes to live in salt water after years of fresh water living. They also skip the lambda bread, because their stomachs shrink to streamline themselves for travel. Their pupils grow so they can see in the darker ocean as hope fades into the world of night.

When they reach their spawning grounds, they release eggs, which are fertilized externally. The eels are thought to clump together to fertilize the eggs. The eggs nestle into the sargassum to start the cycle again. Then white shores call to the adults and their grey ships pass into the west, because they die. 

Cole also mentioned that they could not get them to breed in captivity. He’s right that they tried to do it for a while, but they did do it in 2006. But it was very involved. They had to simulate a 4,000 mile journey and changes between salt and freshwater.

Ending: So wriggle over your obstacles, be catadromous and be elver vigilant like the European Eel here in Life, Death, and Taxonomy.